Electric glow discharge tube



Oct. 9, 1934.

G. HOLST El AL ELECTRIC GLOW DISCHARGE TUBE Filed Feb. 18. 1931 INVENTORS GILLES H0 MAR JUHAN )RUYVESTEYN JAN HENDRK dzBOER BY MAR E *Eves Patented Oct. 9, 1934 UNITED STATES PATENT OFFICE ELECTRIC GLOW DISCHARGE TUBE Gilles Holst, Mari Johan Druyvesteyn,

Jan

ware

Application February 18, 1931, Serial No. 516,546 In the Netherlands February 25, 1930 3 Claims.

This invention relates to an electric glow discharge tube. vapour filling and an independent discharge are used for various purposes, for example, as signal 5 lamps and relays for translating electric current variations into light variations, as used in apparatus for receiving images transmitted telegraphically or by wireless.

With glow discharge tubes of this type frem quently the drawback is prevalent that the tension at which the discharge is initiated, is rather high. This starting voltage is materially greater than the working voltage, i. e., the potential difference between the electrodes after the discharge has been initiated. It has been proposed already to reduce the starting and the working voltage by covering the cathode of the tube with an alkali metal.

The invention has for its purpose to reduce 2% these voltages still further and in addition to improve other properties of the tubes.

The electric glow discharge tube according to the invention has an electrode containing an alkali metal which is provided on a layer of alkali M metal oxide of the composition B20, in which R denotes an alkali metal. In this glow discharge tube not only the starting and the working voltage, but also the internal resistance are exceedingly low, whilst the electrode which is coated with alkali m tal disintegrates but slightly. An additional advantage, which becomes particularly marked it the tube is used for receiving images, for example in television apparatus, consists in that candle power per watt consumption,

35 which is emitted by the luminous glow discharge, is material. By a proper choice of the gas filling the afterglow of such tubes, i. e. the continuation of the luminous discharge after the intensity of the current passing through the tube has been changed, may substantially entirely be avoided.

Probably the afterglow of a glow discharge tube according to the invention which is filled, for example, with neon, lasts less than 0.00001 second.

The working and the starting voltage of the glow discharge may be reduced still further by using a gas filling constituted by a mixture of a gas, for example, neon, and another gas, for example, argon, whose ionization potential is smaller than the excitation potential of neon.

Furthermore the starting pressure of the glow discharge may be reduced to advantage by exposure of the electrode which is coated with alkali metal.

The invention will be more clearly understood by reference to the accompanying drawing, repre- Tubes of this type having a gas or senting, by way of example, one embodiment of the invention.

The illustrated discharge tube which may be used as signal lamp, has a vitreous wall 1, to which a stem 2 is sealed, on which two electrodes are mounted. One of these electrodes is constituted by a metal ring 3, which is carried by a supporting wire 4. The other electrode 5, which is carried by the supporting wire 6, is constituted by a plate made, for example, of copper. At the side which is turned to the electrode 3, this plate is coated with a layer of caesium oxide of the composition C520, on which a layer of caesium is provided. If desired the other side of the plate, just as the supporting wires 4 and 6, may be covered with an insulating material, for example, aluminum oxide.

Some methods of producing the surface of the cathode 5 will hereinafter be described.

After the electrodes have been mounted in the tube and after the latter has been exhausted a small quantity of caesium may be introduced into the tube, which is deposited on the plate 5. The caesium may be introduced into the tube, for example, by evaporation from a vessel which communicates with the glow discharge tube. A suitable method of introducing caesium into the tube, is described, for example, in the patent application 360,993 which issued as Patent No. 1,797,131. After the caesium has been introduced into the tube, oxygen is admitted in excess into the tube, so that the caesium is oxidized due to which C520; is formed. After the excessive quantity of oxygen has been removed from the tube, a fresh quantity of caesium is introduced into the tube, by which the C5204 is reduced so as to form C520. This reduction may be facilitated by heating to about 200 C. The C520 formed may be recognized by its golden brown color. If the caesium is present in excess, it is deposited on the C520 formed. If the caesium is not present in excess, 2. fresh quantity of caesium is introduced into the tube, which is deposited on the layer of caesium oxide formed. Thereby the free caesium will be partly adsorbed by the caesium oxide.

After the first introduction of the caesium it is also possible to admit a dosed quantity of oxygen into the tube, so that the caesium is oxidized so as to form C520, whereupon a fresh quantity of caesium is introduced into the tube, which is deposited on the layer of caesium oxide formed.

Furthermore it is possible to cause the copper plate 5 to adsorb a water layer by introducing some water vapour into the tube. Ir caesium is added in excess after the excessive water vapour has been removed from the tube, the caesium reacts with the water, whereby C830 is formed and hydrogen is liberated which may be removed from the tube, whilst the excess of caesium is deposited on the caesium oxide layer formed.

Although in the methods described hereinbei'ore use is made of caesium it will be obvious that same may also be carried out in combination with the other alkali metals.

Aiter the cathode has been finished the tube is filled with a suitable gas or vapour filling. Satisiactory results have been obtained, for example, with a gas filling at a pressure oi 8 millimetres and constitutedby neon and 0.2% of argon. The starting voltage of this tube, in which the distance between the electrodes may be assumed as being 8 millimetres, for example, will be found to be exceedingly low. When operating the tube in the dark, a starting voltage 01' approximately 56 volts is all that will be required. By irradiating the cathode of the glow lamp by means of a light beam, whereby the exposure of the cathode was 0.015 lumen cm the starting voltage was 54 volts, whereas the working pressure of the glow discharge tube appeared to be 37 volts.

When irradiating the glow lamp by means of a separate light source, it may be advisable to use the same light source for the irradiation of several glow lamps. It is also possible to construct the light source and the glow lamp soas to form an aggregate.

Having now described our invention, what we claim and desire to secure by Letters Patent is the following:

1. A method of operating glow discharge tubes having a pair 01 electrodes upon one of which is a layer of alkali metal oxide which comprises applying a potential diflerence irom a source across the tube electrodes and subjecting the alkali metal oxide electrode to'lightduring the period diameter as the opening in the annular anode electrode so that upon an application of an electric potential difierence between the electrodes glow discharge takes place, and a coating or an alkali metal oxide of a composition R20, where R denotes an alkali metal, upon the surface of the disk-like cathode electrode adjacent the anode for reducing the striking potential.

3. An electric glow discharge tube having a cathode coated with an alkali metal 01! a composition R20, where R denotes an alkali metal, an annular anode electrode arranged coaxial with the cathode through which light from an external source may be applied to the cathode, and a gaseous filling contained within the tube so that upon an application of a potential difference between the anode and cathode electrodes glow discharge is produced and the striking potential is decreased in accordance with the intensity of light influencing the light sensitive porton of the cathode.

GILLES HOLST.

MARI JOHAN DRUYVESTEYN. JAN HENDRIK DE BOER. MARTEN CORNELIS TEVES. 

